The invention relates to a device for the dosed diffusion of gases in liquids, consisting of a diffusor which can be filled with gas via an inlet device and round which liquid circulates.
Diffusion devices of the type mentioned are used, for example, in chemical process engineering and for water treatment. They conventionally consist of a cylindrical diffusor round which liquid circulates and which is filled with the desired gas via an inlet device. In this way, an interface via which the gas diffuses into the liquid is formed in the diffusor.
A preferred embodiment of such devices is aimed at a small-scale application in the field of aquaria, where the problem arises, above all, of a dosed enrichment of the aquarium water with carbon dioxide (CO.sub.2). In addition to a function as a plant nutrient, carbon dioxide acts in the aquarium water as a chemical equilibrium component in the bicarbonate/carbonic acid system, the optimum establishment of which is of great importance for the biotope of the aquarium. The demand for free carbon dioxide depends on the water volume of the aquarium and on the amount of plant mass occupying it, on the type and intensity of the lighting influencing the assimilation process and on the natural proportion of chemical equilibrium carbonic acid (carbonate hardness). The establishment of a supply of CO.sub.2 can be checked by measuring the pH value of the water.
A known device for the diffusion of CO.sub.2 in aquaria consists of a diffusion cylinder which is mounted in a vertical position against the inner wall of the aquarium by means of a suction-cup system, for example two suction cups attached laterally. The upper end face of the diffusion cylinder is designed as a diffusion diaphragm, via which the gas dissolves directly into the water. For this purpose, the diaphragm must be completely covered with water and be located preferably at a height of approximately 4 cm below the water level. The diffusion cylinder is filled via a hose connection piece moulded onto the cylinder casing near the diaphragm. During the filling operation, water standing in the diffusion cylinder is displaced by CO.sub.2 over-pressure. Provided for this purpose in the end face lying opposite the diaphragm is a bottom orifice, through which water flows, even during the gradual diffusion loss of CO.sub.2, in a pressure equilibrium. To check the filling level, the diffusion cylinder is made of glass or a transparent plastic. Filling is carried out by hand, in portions, by means of a regulating valve in which a CO.sub. 2 cartridge is accommodated. Such a diffusion cylinder has to be filled up manually with CO.sub.2 at least once a day.
A diffusion device of this type has a series of disadvantages. On the one hand, the size of the diffusion diaphragm is predetermined owing to the construction, so that the diffusion rate can be adapted to the actual CO.sub.2 requirement only by means of a complicated parallel connection of several diffusion cylinders. Adaptation to a varying CO.sub.2 requirement requires expensive and disturbing modifications in the aquarium. Furthermore, according to the findings of the present invention, the diffusion operation is at its most effective at a high pressure acting on the boundary layer between the gas and liquid. In the known embodiment, however, the diffusion diaphragm is located near the water surface, that is to say, precisely in the region of the lowest water pressure. Measurements on the known diffusion cylinder gave the surprising result that at least a part of the CO.sub.2 diffusion takes place not via the diaphragm, but via the pressure-stabilised gas/water boundary layer at the bottom of the gas column. Finally, the manual filling of the diffusion device according to the state of the art regularly requires the attention of an attendant. However, an outlay of this type is hardly acceptable for commercial breeding aquaria and for decorative aquaria in business premises and restaurants. Filling of the diffusion cylinder by hand will always be accompanied by extreme variations in the level and occasional irregularities which have an adverse effect on the constancy of the CO.sub.2 diffusion rate.